As an apparatus for smoothly coating an adhesive on a band-shaped support, there has been widely available a die coating apparatus by which a coating solution including a resin solution and the like stored in a pocket 21 of a die 8 is fed out of an outlet of a slit 4 onto a band-shaped support 5 continuously transported by a backup roll 6 as shown in FIG. 8. For a common die coating apparatus, there is used a die in which the inclination angle θ of a side end part of a lip of a downstream-side bar 101a is an acute angle or a right angle as shown in FIG. 6.
In order to uniformly coat a coating solution on a band-shaped support continuously transported by a backup roll with the die coating apparatus, it is important to coat the coating solution while causing crosslinking with stability, with the film thickness of the coating solution set constant from the lip tip part to the band-shaped support. Under such circumstances therebehind, in Patent Document 1, the height of the lip of the upstream-side bar is set larger than that of the downstream-side bar of the die, so that a high-concentration high-viscosity non-Newtonian dispersion is uniformly coated. Whereas, in Patent Document 2, the length of the base of the lip of the upstream-side bar of the die is specified to be 20 μm to 100 μm, and the angle formed between the front wall surface of the lip of the upstream-side bar and the slit is set at 45° or less. Thus, the step unevenness of the coating solution is suppressed.
In Patent Document 3, in a die coating apparatus for coating a plurality of coating solutions in a multilayer form, the length of the base of each lip of the die is set long from the downstream side to the upstream side of the direction of transportation of the band-shaped support. Whereas, in Patent Document 4, in a die coating apparatus for coating a plurality of coating solutions in a multilayer form, the gap between each lip and the band-shaped support is set at a value larger than a value three times the length of the base of each lip, and smaller than a value fifty times the length thereof, whereby the step unevenness of the coating solution is inhibited.
However, even when coating is carried out with the die coating apparatus using the die having each lip shape according to Patent Documents 1 to 4, skinning occurs at the end of the lip. Thus, unfavorably, defects such as lateral steps or stripes occur on the coated surface due to the skinning.
Whereas, in Patent Document 5, there is shown a die for extrusion in which the incline angles θ of the side end parts of lips of the upstream-side bar and the downstream-side bar of the die are an acute angle, and the shapes of the lips are symmetrical with respect to the slit. Owing to such a lip shape, the coating solution can be prevented from being left at the tip of the die, whereby a coating layer having smooth surface can be formed. However, even in the case where the die having the lip shape described in Patent Document 5 is used for coating, when the wet layer thickness of the coating solution becomes as large as 300 μm to 3000 μm, the gap between the lip and the band-shaped support is required to be increased larger than the wet layer thickness. Thus, in such a case, unfavorably, the coated surface becomes less likely to be stabilized.
In view of the above-described situation, it has been demanded for a long time to provide a solution which enables preventing skinning by the coating solution so as to form a coating layer having smooth surface as long as possible, and stably produces a resin sheet or the like having favorable surface conditions even when the thickness of the wet layer is as relatively large as 300 μm to 3000 μm.    Patent Document 1: JP-A-2003-53232    Patent Document 2: JP-A-2007-75798    Patent Document 3: JP-A-2002-136909    Patent Document 4: JP-A-2002-153797    Patent Document 5: JP-A-2000-167461